The blades on wind turbines, and to some extent nacelles, are now made of composites, often fiberglass reinforced plastics (FRP) and in some cases carbon fibers. When these components come out of a mold, they require a little grinding and milling that put dust and debris into a plant’s air. Although workers wear respirators, some of that dust can be carried to other places in the facility. Conventional ventilation just uses massive amounts of air to remove the dust, which is fine in the cool days of spring and fall. But on hot and cold days of the rest of the year, there should be more efficient ways of dealing with large amounts of in-plant dust.
State-of-the-art systems go beyond simple air delivery. They use digital controls and energy saving heat-recovery devices to reduce emissions, control dust from grinding and provide workers with the ideal temperature for comfort and the process. Ventilation systems are so sophisticated and energy efficient, they have turned what is traditionally a plant’s least desirable work area into a show room.
All manufacturers and fabricators must comply with EPA and OSHA regulations as well as similar state regulatory authorities regarding the emission of styrene, which is released in the plant work space and into the environment during manufacturing.
In the U.S., OSHA PEL (permissible exposure levels) requirements for styrene require that the breathing zone within the workplace average less than 50 ppm (parts per million) over an 8-hr period.
“Here in Manitoba, if a plant averages over 20 ppm, workers must wear a respirator, where as if you were in North Dakota – just south of us – you would not have to,” says John Zadro, president of Structural Composite Technology. “And if you were in Ontario or Alberta or Saskatchewan, they wouldn’t have to either.”
The reason conventional systems don’t work well, whether removing dust or fumes, is because inadequate or inaccurate information about the quantities was used in engineering calculations. This industrial survey is critical for both types of contaminates and quantity.
To meet the requirements, Zadro installed a state-of-the-art ventilation system when the company moved to a new, larger facility in November of 2007.
For manufacturers like Zadro, the first question might be: Where do I look for new ideas in ventilation? Typically, such systems have been designed and constructed by general HVAC contractors. However, these systems are not designed specific for the needs of FRP manufacturers. Eventually, Zadro selected equipment from Frees Inc. in Shreveport, Louisiana.
Dilution ventilation versus directed air flow
Most ventilation systems depend upon dilution ventilation to meet OSHA’s PEL requirements. Its premise is to bring in enough fresh air to dilute the styrene levels.
Unfortunately, dilution ventilation typical demands a tremendous volume of outside air heated to 70 to 75°F and then exhausted. Furthermore, if a worker is in a concentrated emissions zone, the technique makes it difficult to get air to a particular corner.
According to Zadro, the Frees system he installed is not based on dilution ventilation, but rather a directed air flow to ventilate the breathing zone of the worker, not the entire building.
Frees’ proprietary designing directs a flow that captures contaminated air and focuses it in a controlled envelope moving it across a breathing zone. Air is then removed from the area to prevent roll back and re-contamination of the work are. The contaminated air is forced out high enough for dispersion or routed through an end-of-stack control as mandated by the user’s emission permit.
“The analogy is blowing air around a lit candle to get rid of the smoke, while not affecting the flame. With this system, our shop is regularly less than 20 ppm,” says Zadro.
A directed air-flow system requires 40 to 60% as much air as a conventional ventilation system. Hence, the system demands less equipment, lower operating costs and maintenance, and it typically costs less than conventional systems.
Dust control for trimming, grinding
A dust-control system in a trimming and grinding area can greatly improve working conditions while containing dust that could affect nearby plant functions. A state-of-the-art dust control system transports fiberglass particles away from workers and collects it for proper disposal. The system then re-circulates clean air back to the work area.
Structural Composite Technologies operates two grinding booths. The company produces large fabrications such as vessels, stacks, essentially a four-wall chamber without roof, tanks and other process equipment. The company’s large grinding booth holds parts large enough to require a bridge crane.
“The ventilation system blows air over a part and captures dust so it doesn’t fly out the top or to the rest of the shop,” says Zadro.
Automatic controls and monitoring
Digital controls, such as those supplied by Frees Inc., provide another way to minimize costs. Controls can sense styrene in the air and ventilate accordingly resulting in an estimated 30 to 60% or more energy cost savings.
The system cycles equipment off or reduces its operation to minimum levels when a styrene producing activity ceases. This is accomplished several ways, including motion sensors, monitoring resin flow, or other methods that fit the customer’s manufacturing process.
“Our previous ventilation system would run constantly, but the new one only operates when needed, making it more energy efficient,” says Douglas Caudle, president of Piedmont Fiberglass in North Carolina. “We actually quadrupled the size of our facility, but our energy bill remained the same.”
Digital controls also let fabricators monitor and control the process through a web browser, to turn aspects of the system on and off, adjust temperatures or change timers.
The controls help Piedmont Fiberglass reduce energy costs during three non-production days each week. “On winter weekends, we let the plant cool down. Then on Sunday afternoons, the controls turn the heat up so when the workers arrive, the plant is at operating temperature,” explains Caudle.
One benefit of a state-of-the-art ventilation system is facility cooling and heating to keep the shop at the recommended 70 to 75°F for worker comfort and the process. Constantly warming sub-zero degree incoming air would require exorbitant energy costs, as would constant cooling on a muggy 90°F day.
Today’s ventilation systems use heat recovery equipment to warm incoming air with the heat of discharged air.
Filed Under: Nacelle, News